1. Field of the Invention
The present invention relates to an electro luminescence display device, and more particularly to a fabricating method and apparatus thereof for preventing the deterioration of picture quality.
2. Description of the Related Art
Recently, various flat panel displays have been developed. Flat panel displays have the advantages of reduced weight and reduced bulk over a Cathode Ray Tube (CRT). Such flat panel displays include a Liquid Crystal Display (LCD), a Field Emission Display (FED), a Plasma Display Panel (PDP), and Electro Luminescence (hereinafter, EL) display device.
The structure and fabricating process of the PDP is relatively simple compared to the LCD, FED and EL devices. Another advantage of the PDP is that it can be made to have a large size but yet be lightweight. However, the light emission efficiency and brightness of a PDP are low while its power consumption is high.
Compared to a PDP, an LCD is difficult to make because of the semiconductor processing for making the Thin Film Transistor (TFT), which is used as a switching device in each of the pixels in the LCD. The demand for LCDs has been increasing with the increasing demand of notebook computers because it is typically used as the display device of a notebook computer. However, the LCD has a disadvantage in that power consumption is high because the LCD uses a backlight unit. Further, the LCD also has the disadvantage of high light loss caused by the use of optical devices, such as a polarizing filter, a prism sheet, a diffusion panel. Another disadvantage of the LCD is a narrow viewing angle.
EL display devices are generally classified as either an inorganic EL device or an organic EL device depending on the material of a light-emission layer of the EL display device. Since an EL device is a self-luminous device, it has the advantages of a fast response speed, a high light-emission efficiency and high brightness. In addition, an EL device has the advantage of a wide viewing angle.
FIG. 1 is a sectional view representing an electro luminescence display device of the related art. As shown in FIG. 1, the organic EL display device includes a hole injection layer 22, a light emission layer 24, an electron injection layer 26 deposited between a cathode 28 and an anode 20 on a substrate 2. If a drive voltage is applied across the anode 20 and the cathode 28 in the organic EL display device, holes in the hole injection layer 22 and electrons in the electron injection layer 26 move into the light emission layer 24 and excite a fluorescent material within the light emission layer 24. Accordingly, a picture or an image is displayed by the visible light generated from the light emission layer 24 when a plurality of EL display devices are used together in an active matrix EL display panel.
FIG. 2 is a circuit diagram representing a sub-pixel of an electro luminescence display device of the related art. As shown in FIG. 2, the active matrix EL display panel using the EL display device includes sub pixels 150 each arranged at each intersection area of gate lines GL and data lines DL. Each sub pixel 150 receives a data signal from the data line DL and generates light corresponding to the data signal when a gate pulse is applied to a gate line GL. Each sub-pixel 150 includes an EL cell OEL having its cathode connected to a ground voltage source GND, and a cell driver 152 connected to the gate line GL, the data line DL, a supply voltage source VDD and to the anode of the EL cell OEL for driving the EL cell OEL. The cell driver 152 includes a switch thin film transistor T1, a drive thin film transistor T2 and a capacitor C.
The switch thin film transistor T1 is turned on to apply a data signal applied to the data line DL to a first node N1 when a scan pulse is applied to the gate line GL. The data signal applied to the first node N1 charges the capacitor C and at the same time is applied to the gate terminal of the drive thin film transistor T2. The drive thin film transistor T2 controls the amount of current I applied to the EL cell OEL from the supply voltage source in response to the data signal applied to the gate terminal such that the amount of light emission from EL cell OEL is controlled. The EL cell OEL sustains light emission, even though the switch thin film transistor T1 is turned off, by current I provided to EL cell OEL from the supply voltage source through the drive thin film transistor T2 until the data signal of the next frame is applied because the voltage of the data signal is maintained by the discharging of the capacitor C.
FIG. 3 is a plan view of the cell driver shown in FIG. 2. As shown in FIG. 3, a relate art cell driver includes a drive thin film transistor T2 formed adjacent to an intersection of the gate line GL and a supply line RL. Further, the gate 104 of the drive thin film transistor T2 is connected to a switch thin film transistor T1. The switch thin film transistor T1 includes a gate electrode 130 formed of the gate line GL, a source electrode 106 from the data line DL, a drain electrode 108 connected through a connection contact hole 118 to a gate electrode 104 of the drive thin film transistor T2, and an active layer 102 forming a conduction channel between the source electrode 106 and the drain electrode 108 when a voltage is applied to the gate electrode 130. The active layer 102 is connected to the source electrode 106 and the drain electrode 108 through a first and a second switch contact holes 116a and 116b, respectively.
The drive thin film transistor T2 includes a gate electrode 104 connected to the drain electrode of the switch thin film transistor T1, a source electrode 112 connected to a supply line RL through a supply contact hole 134, a drain electrode 110 connected to a pixel electrode 100 through a pixel contact hole 132, and an active layer 114 forming a conduction channel between the source electrode 112 and the drain electrode 110 when a voltage is applied to the gate electrode 104. The active layer 114 is connected to the source electrode 112 and the drain electrode 110 through a first and a second switch contact holes 120a and 120b, respectively. The drive thin film transistor T2 applies a supply voltage signal VDD from the supply line RL to the pixel electrode 100, which acts as an anode for an organic EL layer (not shown), in response to the data signal from the gate electrode 104. An organic EL layer (not shown) and a cathode (not shown) are sequentially formed on the pixel electrode 100 to complete the organic EL sub pixel.
In the related art, an organic EL layer is patterned and formed by a vacuum deposition method, a coating method using a spray head or a printing system. FIG. 4 is a diagram representing an apparatus for fabricating an electro luminescence display device of the related art using a printing system. As shown in FIG. 4, an apparatus for fabricating a related art organic EL device includes a supply roller 8 having EL material on the supply roller, a print roller 4 having a resin plate 6 for receiving the EL material from the supply roller 8 and a substrate 2 loaded under the print roller 4.
Either red R, green G or blue B EL materials are dropped on the supply roller 8 from a dispenser 10 positioned above the supply roller 8. A blade 16 is positioned close to the supply roller 8 to spread the EL material uniformly on the resin plate 6. The print roller 4, while rotating by a turning force, transfers the EL material on the supply roller 8 to a groove of the resin plate 6 and then the print roller subsequently rotates to print the EL material on the substrate 2.
FIG. 5 is a perspective view of the related art resin plate shown in FIG. 4. FIG. 6 is a sectional view of the related art resin plate shown in FIG. 4. The resin plate 6, as shown in FIGS. 5 and 6, includes a base surface 14 and a first to an nth pattern line SL1 to SLn formed to be projected from the base surface 14. The first to nth pattern lines SL1 to SLn are formed at locations corresponding to a first to an nth sub-pixel area P1 to Pn on the substrate 2 in the same shape as the pixel formed on the substrate 2. As shown in FIG. 5, the pattern lines SL are formed as raised stripes with a designated gap therebetween. On the surface of each of the pattern lines SL, there are formed a plurality of hemispherical shape grooves 30, as shown in FIG. 6. The pattern lines SL contact the supply roller 8 containing the EL material such that the EL material is uniformly spread on the pattern lines SL with a predetermined thickness for transferred onto the substrate 2. A print table 1 having the substrate 2, which is to be printed, is loaded by a loading device (not shown) below the print roller 4. The substrate 2 can already have an electrode pattern and various material layers formed thereon for an EL display device configuration.
After the substrate 2 on the print table 1 is loaded, the EL material is supplied from the dispenser 10 onto the surface of the supply roller 8. The EL material is then provided in the pattern lines SL of the resin plate 6 when the print roller 4 rotates across the resin plate 6. After being printed on the corresponding substrate 2, the EL material is cured to form an EL layer on the substrate 2. In this way, an EL layer of a specific color, such as red, is formed, and then the EL layers of the other colors, such as green and blue, are subsequently formed in the same way.
The first and the nth pattern lines SL1 and SLn among the pattern lines SL of the related art organic EL display device are formed in a different shape from the other pattern lines. That is, as shown in FIG. 6, the side surface of the first and nth pattern lines SL1 and SLn adjacent to the outer area of the base surface 14 has gap with a first depth h1, and the other side surface of the first and nth pattern lines SL1 and SLn adjacent to the other pattern lines has a gap with second depth h2 lower than the first depth h1. The other pattern lines SL2 to SLn-1 except for the first and nth pattern lines SL1 and SLn are formed to have gaps in between that are at the second depth h2.
The different depths of the gaps are caused by a photolithography process that includes an etching process that etches relatively more at the side surfaces adjacent to edges of the base surface 14 as opposed to in between the pattern lines. FIG. 7A to 7C are diagrams representing an organic EL layer formed using pattern lines shown in FIGS. 5 and 6. FIG. 8 is a plan view representing a bad pattern of an organic EL layer formed using the pattern lines shown in FIGS. 5 and 6.
In the event that a red organic EL material is printed using the first and nth pattern lines SL1 and SLn, a bad pattern occurs because the first and nth pattern lines SL1 and SLn are etched relatively more, as shown in FIG. 7A. Thus, there is a problem in that a bad printing occurs in the first and nth red sub-pixel areas R1 and Rn, which are formed at both edge end parts of a display area. In the same manner, in the event of a subsequent sequentially printing of the green and blue organic EL materials, as shown in FIGS. 7B and 7C, there is a problem that bad printing occurs in the first and nth green sub-pixel areas G1 and Gn and in the first and nth blue sub-pixel areas B1 and Bn, which are both formed at edge end parts of a display area. Thus, as shown in FIG. 8, there is a problem in that bad picture quality occurs in the first and nth pixels P1 and Pn, which consist of a red R, a green G and a blue B sub-pixels having a badly printed organic EL layer. Because it is difficult to fix specific areas of the organic EL display device, the organic EL display device may have to be discarded.